test padding units for non-stacked bubble chart
test padding units for non-stacked bubble chart

for #1234

TheDataShed/dc.js,mtraynham/dc.js,aaronhoffman/dc.js,mtraynham/dc.js,dc-js/dc.js,dc-js/dc.js,aaronhoffman/dc.js,aaronhoffman/dc.js,TheDataShed/dc.js,dc-js/dc.js,mtraynham/dc.js,TheDataShed/dc.js,aaronhoffman/dc.js,TheDataShed/dc.js,dc-js/dc.js,aaronhoffman/dc.js,mtraynham/dc.js,dc-js/dc.js,mtraynham/dc.js,TheDataShed/dc.js